Has an AFL game ever ended 23-18?
Exactly once. On May 26, 1900, Essendon beat Carlton 23-18, and no AFL game before or since has ended that way. When it happened it was a scorigami, the first 23-18 in league history.
That makes 23-18 the 3884th most common final score out of 6,649 that have ever occurred in AFL. One point away, 24-18 has happened never and 23-19 has happened never.